1. Field of the Invention
The present invention relates to a film formation method and apparatus for a semiconductor process for forming a silicon oxynitride film (SiON film) on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices, a process, such as a heat process or CVD (Chemical Vapor Deposition), is performed to form a thin film, such as a silicon nitride film or silicon oxynitride film, on a target substrate, such as a semiconductor wafer. For example, Jpn. Pat. Appln. KOKAI Publication No. 5-251428 (Patent Document 1) discloses a method for forming a silicon oxynitride film by a heat process. This method comprises a step of forming a silicon oxide film on a target substrate within a reaction chamber, and a step of nitriding the silicon oxide film on the target substrate within the reaction chamber.
In recent years, semiconductor devices have been increasingly miniaturized, and thus silicon oxynitride film are required to be thinner. As silicon oxynitride films are thinner in semiconductor devices, small fluctuations of the nitrogen concentration in the silicon oxynitride films have a larger effect on electrical characteristics of the devices. For example, in the case of a vertical heat processing apparatus of the batch type, the nitrogen concentration in formed silicon oxynitride films is reduced only by replacement of members inside a reaction chamber. Since the nitrogen concentration in the silicon oxynitride films thus changes, the electrical characteristics of devices that contain such films also fluctuate.